1. Field of the Invention
The invention relates in general, to springs, and in particular to a new and useful pressure spring tensioner, for the tightening of axle springs in motor vehicles. In particular, the invention includes a cylindrical guiding tube with a threaded spindle mounted rotatably therein and two gripping clamps, a first gripping clamp being fixedly fastened to one end of the guiding tube by means of a sleeve and a second gripping clamp being mounted to a second sleeve which is axially movable. The second clamp encloses the guiding tube with a sliding snug fit. The second clamp includes a sleeve being connected to a sliding pad by means of a radial finger protruding through an axial slit of the guiding tube, the slit being open at one end. The sliding pad is axially movable on the inner surface of the guiding tube and it is engaged with the threaded spindle by means of an inner threading.
In a known pressure spring tensioner as described in German patent No. (DE-PS No. 28 13 381) the cylindrical guiding tube has two diametrically opposed axial slits or openings through which radial fingers of the sliding pad protrude toward the outside and are supported on one of several transverse shoulders of the sleeve. These transverse shoulders are formed by recesses having the same width as the radial fingers and the axial slits.
While the slaving of the movable sleeve by the sliding pad in the tensing direction of a spring to be tensed is effected by the supporting of the transverse shoulders of the sleeve on the radial fingers of the sliding pad, one of the radial fingers is connected to the sleeve by means of a screwed-on bracket or shackle. In the known pressure spring tensioners this connection is a weak point because, during a machine-operated actuation of the threaded spindle in the relaxing direction of a tightened spring, the screw-connection between the bracket and the radial finger, or between the bracket and the sleeve always breaks. The breakage is due to a lack of attention of the gripping clamp rotating in the direction of the spindle head during relaxation of a spring mounted in a vehicle when it catches on a fixed object, e.g. the bottom spring reception, and the spindle is rotated further nevertheless. This often necessitates awkward and time-consuming repairs which usually entail an exchange of the sliding pad as well as of the sleeve.
Further weak points of the known pressure spring tensioners, which often lead to defects and repairs, result from the mounting of the threaded spindle in the guiding tube. The threaded spindle has smooth, tapered cylindrical sections at both ends, each of which is mounted in an axial thrust bearing. The threaded spindle is supported on the axial thrust bearing which is arranged at the end opposite the head of the static rod (at the bottom end of the static rod) by means of a traverse pin which is calibrated for a specific axial shearing force, and therefore forms a predetermined breaking point. The opposite end section has a key head pinned to the threaded spindle. The pin connection between the key head and the threaded spindle is also supposed to serve as a predetermined breaking point, in particular for the case that the threaded spindle is rotated further in the relaxation direction even if the movable gripping clamp has run into a non-yielding obstacle and the distance between the two gripping clamps can no longer be increased. In practice, however, it has turned out that even such a predetermined breaking point can entail difficult, time-consuming and therefore expensive repair if it breaks.